1. Field of the Invention
This invention relates to an improved process for bonding cellulosic and/or ligno-cellulosic materials in the production of synthetic board products by utilizing an internal release agent-containing polyol/polyisocyanate binder.
2. Description of the Prior Art
Many board products are manufactured by the basic process of consolidating or joining together bodies of cellulosic and/or ligno-cellulosic materials or furnish using pressure, heat and a chemical binder. Typical binders used in making such products are thermosetting resins such as phenol-formaldehyde, resorcinol-formaldehyde, melamine-formaldehyde, urea-formaldehyde, urea-furfural and condensed furfuryl alcohol resins. Another binder system, which has been gaining favor in recent years, involves the use of organic polyisocyanates, either alone or in combination with other binder materials, such as urea-or melamine-formaldehyde resins, phenol-formaldehyde resins, etc.
The use of polyisocyanate binders in the production of board products is subject to the drawbacks that the isocyanates generally are more expensive than the commonly used formaldehyde binder systems, and the boards produced with the isocyanates have a tendency to adhere to the face of the platens used in their formation. This adhesion can damage or even ruin the board product, and the subsequent cleanup of the contaminated platens is difficult, time-consuming and costly.
Various attempts have been made to overcome this adhesion problem. Conventional release agents such as oils, wax polishes, silicones and polytetrafluoroethylene have been tried and found wanting. U.S. Pat. No. 4,100,328 discloses the use of a polyether polyol-organic polyisocyanate binder composition for bonding cellulosic materials and eliminating sticking to mold faces. Unfortunately, in this binder composition a portion of the rather costly isocyanate component is replaced by polyols which themselves are relatively expensive materials. It accordingly would be highly desirable if a binder system for board products could be prepared by combining an isocyanate with a relatively inexpensive diluent which significantly reduces the overall cost of the system but still contributes to the obtainment of desirable board properties, including superior strength, moisture resistance and release.